A microbiological and molecular study of the microbial community involved in restoring mining wastes using isolation and high throughput sequencing.

Soutenance de thèse de Najoua Mghazli le 8 mai 2023

Résumé : The mining sector produces large amounts of wastes that have detrimental effects on the environment and Human health. When sulfur-containing minerals are present, acidic effluents containing generally toxic metallic pollutants, also known as Acid Mine Drainage (AMD) are produced. The oxidative breakdown of sulfide minerals and the subsequent production of AMD are significantly accelerated by microorganisms. To protect environment from reactive mining tailings, it is important to identify and understand the activity of microbial communities. The pyrrhotite Kettara mine in Morocco has produced more than 3 Mt of wastes, that negatively impact the 2000 residents of the Kettara village, by formation of AMD, sulfur emanations and windblown of toxic dust. The rehabilitation scheme of this mine consists of the use of a store-and-release phosphate mining waste cover on top of acid and polluted mining wastes. The final step is the revegetation of the phosphate wastes. Morocco holds the vast majority of the world’s phosphate reserves and produced millions of tons of mining wastes each year. The revegetation is an efficient and cost-effective tool for stabilizing and reintegrating wastes to their surrounding ecosystem, but their very poor-quality prevents the establishment and the growth of plants, particularly in semi arid area. However, microorganisms can significantly speed up the phytostabilization process. The goal of this thesis was to provide a better understanding of the role played by microbial communities in both the production of AMD systems, which is the source of pollution in Kettara, and microbial communities involved in revegetation of phosphate mining wastes, a national priority for Morocco. High throughput sequencing techniques were used for the first time to examine the diversity and metabolic potential of microbial communities for these types of wastes in Morocco. A quite unusual microbial communities were identified in the Kettara pyrrhotite mine tailings and we evidenced the potential presence of a high number of strains that could facilitate plant development by metagenomic prediction and literature analysis. Plant-growth promoting activities of isolated bacterial strains were also tested in vitro and, in planta for the best performing bacteria. A strong PGP activity of Stenotrophomonas rhizophila and for the first time for Brevibacterium anseongense was observed for the growth of Lupinus albus L., demonstrating their potential use as biofertilizer.